The present invention relates to a flat type display device in the form of a liquid crystal panel, an organic EL panel or a plasma panel, for example, and, more particularly, the invention relates to a method of inspecting control signals for these display devices, and a display unit having this inspecting function.
In an image and screen image display unit using a flat type display device, such as a personal computer or a flat panel type television, for example, various kinds of timing signals serving as control signals for displaying a display signal (an image signal and a screen image signal) on the screen of the display device are supplied from an external signal source (HOST), such as an image processing circuit of a personal computer main body or a screen image signal processing circuit of a television receiver, etc., together with the display signal.
When there is an abnormality in the control signal inputted from the external signal source, an abnormality is produced in the screen display of the display device. An oscilloscope or a logic analyzer is conventionally used to inspect for such an abnormality of the control signal. However, there is a limit in the amount of information that is able to be stored by the oscilloscope or the logic analyzer. Further, it takes time and labor to detect whether the abnormality exists in the control signal corresponding to which location on the display screen. The measurement is easy when it is to determine whether it is an abnormality signal or not due to switching of the edge of a vertical synchronizing signal, a horizontal synchronizing signal or a display timing signal. However, it is difficult to measure in which location the abnormality exists within a certain frame.
On the other hand, in the display device of the active matrix type, such as a liquid crystal display unit of a thin film transistor type (TFT-LCD), for example, screen image information is displayed on the screen of the display device in real time, but it is impossible to display how its control signal is constructed on the screen. When a normal display is produced, no display of the control signal is required. However, when the display is abnormal, it is not easy to determine how the abnormality signal is inputted from the external signal source, even when it is possible to judge whether this abnormal display exhibits an abnormality of the screen image information or an abnormality of the control signal. Reference is made to literature 1 (JP-A-2001-109424) or literature 2 (JP-A-2001-272964), which disclose techniques for coping with a control signal abnormality of this kind.